I cobbled the engines together by chopping up a Wingnut Wings BMW engine from their Fokker D.VII (available from them as a separate sprue). It is not entirely accurate in detail, but a rough representation in terms of shape and size. I wasn't that interested in spending the time necessary to scratch-build the two engines, especially considering that most of the detail is hiddenh-build two engines.
Wow Steve very nice model. If I'm correct the first time I saw one of your model it was in the charter issue of Finescale Modeler (Spring 1982) a scratch built M1 Abrams, I still have the issue.